Written by: Bethany Beekly
Editors: Christina Del Greco, William Dean, Olivia Pifer Alge, and Madeline Barron
…Then this ebony bird beguiling my sad fancy into smiling, By the grave and stern decorum of the countenance it wore, “Though thy crest be shorn and shaven, thou,” I said, “art sure no craven, Ghastly grim and ancient Raven wandering from the Nightly shore— Tell me what thy lordly name is on the Night’s Plutonian shore!” Quoth the Raven “Nevermore.”
While Poe’s raven is generally understood to be metaphorical, the premise of his famous tale is not outside the realm of possibility. Ravens belong to a family of birds called corvids (Latin Corvidae) which also includes other common urban birds such as crows and magpies. Corvids are among the most intelligent avian species studied to date. They also happen to be among the select families of birds capable of mimicking human speech!
Vocal mimicry is a complex phenomenon which consists of a “model” sound to be copied, and a “mimic” organism that hears and subsequently learns to reproduce the model sound. Importantly, this type of learning is distinct from the process that enables birds to acquire the stereotypical calls of their own species. Arguably science’s most famous talking bird, Alex (short for “avian language experiment”) the African gray parrot, learned to say more than 100 words over the course of his life with handler Irene Pepperberg. Another renowned mimic, the superb lyrebird, wreaks havoc in zoos by mimicking the sound of fire alarms and screaming children, but also uses its talents in the wild to secure a mate: a male will mimic the sound of a multi-species flock of birds sounding alarm calls to scare his desired mate out of flying away. By making her think there is a predator nearby, he ensures she will remain still long enough for him to engage in his unusually-long copulation ritual.
No matter how many hours I spend listening to bird calls, I cannot physically produce the sounds that would be necessary for me to convincingly mimic them—even though I might learn to recognize them if I hear them. So why are some birds capable of mimicking human speech? It turns out birds have a unique vocal mechanism that enables them to generate an extraordinary variety of sounds. Humans (and other vertebrates) produce vocalizations via the larynx, an organ which also facilitates respiration by protecting the airways. The larynx has just one pair of vocal folds, which limits the range of possible vocalizations. Birds have a larynx, too, but they don’t use it to vocalize; instead, they use a special organ called a syrinx. The syrinx has not one but two pairs of vocal folds. It also resides much deeper in the airway than the larynx, at the point where the trachea branches into two tubes leading to the lungs. The combination of multiple pairs of vocal folds and multiple passages for flowing air means the syrinx can actually produce different sounds simultaneously from the right and left sides! However, a complex vocal mechanism is not the only predictor of whether an animal will be able to engage in vocal mimicry.
While all birds have a syrinx, they do not all engage in mimicry—to date, this behavior is observed only in oscine songbirds (including corvids), parrots, and hummingbirds. To understand why this is, we must turn to the neural circuits involved in vocal learning. Humans and certain birds share a lot of similarities in the way they learn to speak and sing that set us apart from other vertebrates. Most animals have species-specific motor programs for innate vocalization and do not actually need auditory feedback to learn them, meaning even if they grow up with no individuals of the same species to listen to, they are still able to generate their stereotypical sounds. A motor program is a kind of shortcut that is a bit like a cookie cutter for your brain: it enables you to perform a movement quickly and consistently without significant conscious effort. It does this by outlining which muscles are needed for a type of movement, and approximately how and in what order they move in relation to each other. Context-specific tailoring can be layered on top, like using icing or sprinkles to add unique detail to the basic shape of your cookie! The vocal motor programs are situated in the brainstem (the basal part of your brain that joins it with the spinal cord) and are not under conscious control.
Humans and birds capable of vocal mimicry, by contrast, learn to speak and sing by listening to other individuals of their species and engaging a more complex neural circuit that remains incompletely understood. While the details of this neural circuit vary by species, the general structure required for vocal learning seems to consist of two neural pathways: an “anterior pathway” in the front of the brain where the acoustic structure and sequencing of sounds is processed, and a “posterior pathway” in the back of the brain which generates motor outputs to physically generate the sounds and refines them based on how well the produced sound matches the model. This is not necessarily a series of steps—the two pathways are engaged simultaneously. Think of the way a baby babbles while learning to talk: they build an understanding of which combinations of sounds go together to form words, even as they develop their ability to mimic the sounds they are hearing. Adorably, baby birds can “babble” in an extremely similar way! The existence of this more complex learning system which relies on auditory inputs and feedback, combined with their sophisticated vocal mechanism, is why some birds are able to mimic other sounds later in life.
On rare occasions, other vertebrates—typically in zoos and aquaria where animals have close relationships with their human keepers—have been documented mimicking human speech. For instance, seals have been demonstrated to be capable of mimicking many sounds, including the human voice. A famous example is Hoover the harbor seal. A resident of the New England Aquarium from 1971-1985, Hoover delighted audiences by mimicking his rescuer George Swallow, who found him as a pup after his mother died. Recent studies have begun unraveling the neural substrates of vocal learning in grey seals and revealed some similarities between both humans and songbirds. Elephants also seem to share some neuroanatomical features and behavioral traits of vocal learners. One Asian elephant named Koshik even imitated a handful of words in Korean that he heard regularly from his keepers at the Everland Zoo in Yongin. And while they aren’t able to produce the sounds of human speech, some whales, dolphins, and bats can be trained to demonstrate characteristics of vocal learning. But birds remain our most reliable and versatile mimics. Like Poe’s raven, the accuracy and timing with which birds show off their gifts ranges from the humorous to the uncanny. One thing’s for sure: “birdbrain” is not the insult we’ve been led to believe!
- Re-evaluating vocal production learning in non-oscine birds
- The Development of Language: A Critical Period in Humans
- Theme issue of Philosophical Transactions of the Royal Society B: Biological Sciences—‘Vocal learning in animals and humans.’
Bethany Beekly is a Neuroscience student in the Elias Lab (UM Department of Molecular and Integrative Physiology). She studies the interplay between sleep and the neuroendocrinology of reproduction. She is also heavily involved with the Graduate Employee Organization (GEO), serving as Steward for the Neuroscience Program and the Chair of the Climate Caucus. When she isn’t doing science or fighting for worker’s rights, she can often be found outside hiking, camping, reading, doing yoga, or just sitting with a cup of coffee listening to the birds.